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Relationship between Compost Stability and Extractable Organic Carbon

Wu, L., Ma, L.Q.
Journal of environmental quality 2002 v.31 no.4 pp. 1323-1328
absorbance, carbon, carbon dioxide, carbon dioxide production, compost stability, composting, fulvic acids, humic acids, pH, quality control, sodium hydroxide
Establishing a simple yet reliable compost stability test is essential for a better compost quality control and utilization efficiency. The objective of this study was to examine the relationship between extractable organic carbon (OC) and compost stability based on 18 compost samples from five composting facilities. The compost samples were extracted sequentially with water for 2 h [water] and 0.1 NaOH for 2 and 24 h [NaOH and NaOH, respectively]. The extractable OC was further separated into fulvic acid (FA) and humic acid (HA) fractions by adjusting the pH to <2. The mass specific absorbance (MSA) of OC in the six fractions was measured. Compost stability was estimated with a CO evolution method. The extractable OC concentration was influenced by the total volatile solids and decreased with curing time for compost with a high level of extractable OC. The OC levels in each fraction were significantly correlated (< 0.05) to each other except for the water–extractable HA. In addition, all the FA and HA fractions except for water–extractable HA were highly (< 0.01) and linearly correlated to CO evolution, but multiple regression showed that NaOH–extractable OC was insignificant for CO evolution. The relatively high slope of NaOH–extractable FA versus CO evolution suggests that this fraction may contribute the most to compost CO evolution. The water– and/or NaOH–extractable FA tests are recommended for measuring compost stability because of their high correlation with CO evolution. This estimation can be obtained through a simple photometric method covering a wide range of carbon concentrations up to 4000 mg L